Coronary arteries provide blood and nutrients to the heart muscle. The arteries are subject to atherosclerosis or hardening of the arteries. Vascular regions have plaques formed within, resulting in stenosed regions having reduced cross-sectional area. The reduced area causes a reduction in transport of blood, oxygen, and nutrients which can result in angina, myocardial infarction and death.
A commonly used method for treating atherosclerosis is Percutaneous Transluminal Coronary Angioplasty (PTCA). PTCA includes insertion of a balloon catheter through an incision in the femoral artery near the groin, advancement of the balloon over the aortic arch, further advancement within the selected coronary artery, continuing until the balloon portion is placed across the stenosed region. The balloon is inflated, widening the narrowed vessel region.
After catheter withdrawal, significant vessel reclosure may develop. The reclosure may occur within hours or days of dilation, an "abrupt reclosure." When reclosure does occur, however, it more commonly occurs progressively, within six months of the angioplasty. The gradual reclosure is referred to as "restenosis", and largely negates the dilatation treatment. More highly stenosed vessel regions have a greater chance of becoming restenosed.
One approach to dealing with restenosis utilizes stents which are short tubular sections having a lumen therethrough, placed across the recently dilated vessel region. Stents can be either self-expanding or balloon-expandable. Stents are normally left in place indefinitely.
Use of radiation to kill and inhibit growth of cancerous cells is well known. The use of radiation to inhibit restenosis has been proposed. Use of a catheter having a radioactive source on the distal end has been proposed in U.S. Pat. No. 5,199,939 (Dake et al.). The catheter must be held in place during the entire therapy, which is considerably shorter than the months long period over which restenosis is believed to occur. Any radiation delivered must be delivered within the short period the catheter tip is in place. U.S. Pat. No. 5,059,166 (Fischell et al.) proposes using a radioactive stent. As a stent can be left in place indefinitely, the radiation exposure period more closely matches the time period over which restenosis can occur.
Use of a radioactive stent can present drawbacks. A radioactive stent can require shielding both during storage and during placement within the patient. During stent placement, the stent is normally mounted within a delivery device and inserted into the vasculature of the patient. A common entry site is an incision in the femoral artery near the groin. The stent placement procedure is typically performed with several medical personnel present who require shielding if the radiation source is sufficiently strong.
Radioactive stents can have a shelf-life limitation, especially when the radioisotope has a half-life on the same order as the expected shelf life. For example, a stent made radioactive with an isotope having a half-life of about a month will lose half its radioactivity in a month on the shelf. This can present a variation in radiation strength dependent upon the time a stent resides in a warehouse or sits unused in a hospital. The half-life of a radioisotope, if sufficiently small, can preclude its use with stent technology if a significant portion of radioactivity is lost during stent manufacture, shipping and storage. Another limitation with current stent technology is that the stent radioactivity must be decided at the time of manufacture rather than treatment.
What remains to be provided is a method for delivering concentrated radiation at a dilated, stented site without requiring placement of a radioactive stent. What remains to be provided is a device allowing placement of a non-radioactive stent within the vasculature which can be made radioactive in-situ, after placement.